fast2g

well my car is a 90 s5 na the car during the cold start up the voltage is fine
at 14 then when you turn on the ac and the lights it drops down to 12.5
and stays there (i rev the car and it goes up to 13 and drops back 12.5)
then when the idle is at 700 the gauge is reading 12.9 and when i turn on the lights
and the ac the car want to shut off but doesnt. does any one else car do this
or do i need a new alternator.

also the lights flicker and the alternator whines loud.